Fluidmaster Fill Valve I Flush The Toilet I See Water Trickling Down Into The Toilet Bowl For About 15-20 Sec, What Causes This?

I flush the toilet I see water trickling down into the toilet bowl for about 15-20 sec, what causes this? - fluidmaster fill valve

I use a Fluid master fill valve in my house, 2 further bathrooms are not. I am the original case that comes with the filling valve was placed at the same time, the filling valve has about 4 months ago.